In memory applications in the semiconductor industries, such as DRAM and 2D NAND, plasma etching removes silicon-containing films, such as SiO or SiN layers, from semiconductor substrates. For novel memory applications, such as 3D NAND (e.g., see US 2011/0180941 to Samsung Electronics Co., Ltd.), etching of stacks of multiple SiO/SiN or SiO/poly-Silicon (p-Si) layers is critical. An etchant having high selectivity between a mask and the layers being etched is an essential. Furthermore, an etched structure etched by the etchant on the stacks of multiple SiO/SiN or SiO/p-Si layers should have a straight vertical profile without bowing.
Traditional etch gases include octafluorocyclobutane (cC4F8), hexafluoro-1,3-butadiene (C4F6), CF4, CH2F2, CH3F, and/or CHF3. It is well known that selectivity and polymer deposition rate increase as the ratio of C:F increases (i.e., C4F6>C4F8>CF4). See, e.g., U.S. Pat. No. 6,387,287 to Hung et al.
However, traditional etch chemistries may not provide higher aspect ratio than 20:1 necessary in new applications (e.g., 3D NAND) at least due to insufficient etch resistant polymer deposition on sidewalls during plasma etching processes. Here, 20:1 refers to a ratio of the height of a trench (or via) to the width of the trench (or the diameter of the via) being etched. Additionally, —CxFy—, wherein x ranges from 0.01 to 1 and y ranges from 0.01 to 4, polymers on sidewalls are susceptible to etching. As a result, the etched patterns may not be vertical and the etch structures may show bowing, change in dimensions, and/or pattern collapse.
Bowing may result from sidewall etching of the mask layer, which may often be an amorphous carbon (a-C) material. The a-C materials may be etched by oxygen radicals in the plasma which may cause increased opening of the mask and result in bow-like, or angled/curved, etch structures.
Ji et al. (U.S. Pat. No. 5,814,563) disclose using a mixture of fluorohydrocarbon, carbon-oxygen, and NH3-generating gases to achieve high selectivity of dielectric (such as SiO and SiN) to p-Si layers. Shane (US 2003/0162395) discloses addition of nitrogen-comprising gas to fluorocarbon to deposit polymer on mask to improve selectivity while etching silicon dioxide layer. Nemani et al. (US 2014/0199851) disclose using a plasma process performed by flowing NF3 and NH3 to remove the modified portion of silicon nitride layer to pattern a silicon nitride dielectric film. Hamrah et al. (U.S. Pat. No. 5,242,538) discloses using CF4 and NH3 etching gases and selectivity of silicon oxide to polysilicon selectivity of up to 100:1 was observed. Pu et al. (U.S. Pat. No. 5,843,847) also discloses adding additional nitrogen gas to fluorinated etching gas to assist in feature dimensional control.
Nitrogen containing compounds have been used as etching gases. For example, Khandelwal, et al. (“Dry removal technology for advanced CMOS devices”, Nanochip Tech. J., vol. 11, issue 2, 2013, p 17-19) disclose an in-situ dry removal process using NH4F as etchant. Garg et al. (US 2006/0062914) disclose an activated reactive gas to treat the surface of a substrate. Garg et al. describe at paragraph [0019] that the activated reactive gas may include a large variety of fluorine-containing gases, including C3F3N3, fluoroamines such as CF5N, fluoronitriles such as C2F3N, C3F6N, and CF3NO. Felker et al. (U.S. Pat. No. 6,508,948) disclose perfluorinated heteroaromatic amine etching compounds, including cyanuric fluoride compounds. One disclosed cyanuric fluoride compound is pentafluoropyridine C5F5N.
It is important to minimize bowing and to achieve high aspect ratio (i.e., up to 200:1) needed for current applications (e.g., contact etch or 3D NAND). Additionally, etching today has not been limited to selectivity to the photoresist mask. It is equally important to get high selectivity among other materials such as a-C, SiN, p-Si, SiC or other forms of SiaCbOcHdNe materials (where a>0; b, c, d and e≧0).
Thus, a need remains for new etch gas compositions for use in plasma etching applications, which may maintain selectivity and high aspect ratio for a wide range of process conditions.